Method of detecting clutch tie-up during transmission shifting

Abstract

The disengagement of the off-going clutch is monitored to determine as early as possible if there is a clutch tie-up due to failure to disengage. Beginning at the initial clutch release command, the turbine speed and output speed are used to determine if clutch slip has occurred and a pass signal is given if slip occurs in several consecutive control loops. Beginning a preset time after the command to fully exhaust the clutch, the number of no-slip conditions are counted. A fail signal is given when a set number of no-slip conditions are counted.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In a vehicular automatic transmission having an input and an output, a turbine connected to the input to couple driving torque thereto, turbine and output speed sensing means, and electronic control means coupled to the outputs of the speed sensing means, in which a shift from an initial transmission range to a target range requires disengagement of an off-going fluid pressure operated torque transmitting device and failure of such disengagement results in a tie-up condition, and in which the device is controlled by an initial release command and a final exhaust command, the method of testing whether there is a tie-up condition of the off-going torque transmitting device comprising the steps of: determining the absence of tie-up as soon as possible in a shift by periodically testing for slip of the off-going torque transmitting device from the time of the release command and issuing a pass indication when a given number of slip detections occur,   periodically testing for the absence of slip beginning a set time after the exhaust command of the off-going device, and issuing a fail signal when the absence of slip is detected a given number of times, and   terminating the testing when a pass indication is issued.   
     
     
       2. The invention as defined in claim 1 including the step of calculating the product of the initial range speed ratio and the output speed and defining a window centered at the calculated product, wherein slip is detected when the turbine speed is outside said window and the absence of slip is detected when the turbine speed is within the window. 
     
     
       3. In a vehicular automatic transmission having an input and an output, a turbine connected to the input to couple driving torque thereto, turbine and output speed sensing means, and electronic control means coupled to the outputs of the speed sensing means, in which a shift from an initial transmission range to a target range requires disengagement of an off-going fluid pressure operated torque transmitting device and failure of such disengagement results in a tie-up condition, and in which the device is controlled by an initial release command and a final exhaust command, the method of testing whether there is a tie-up condition of the off-going torque transmitting device comprising the steps of: determining the absence of tie-up possible in a shift by periodically testing for slip of the off-going torque transmitting device from the time of the release command and issuing a pass indication as a function of slip detection,   periodically testing for the absence of slip beginning a set time after the exhaust command of the off-going device, and issuing a fail indication as a function of the absence of slip, and   terminating the testing when a pass or a fail indication is issued.   
     
     
       4. The invention as defined in claim 3 including the step of calculating the product of the initial range speed ratio and the output speed and defining a window including the calculated product, wherein slip is detected when turbine speed is outside the window. 
     
     
       5. The invention as defined in claim 3 including the step of testing for slip and the absence of slip by comparing the turbine speed to the product of the initial range speed ratio and the output speed. 
     
     
       6. The invention as defined in claim 3 further including the steps of: when the shift is an upshift, detecting turbine flare by determining when turbine speed exceeds the product of output speed and the speed ratio of the initial range by a set amount, and   generating a pass signal to indicate no-tie-up when turbine flare is detected.